Vtable for Mac startup items

This vtable includes some basic startup items for Mac. The strategies come from KnockKnock (https://github.com/synack/knockknock).

Depends on https://github.com/facebook/osquery/pull/285
can you change this to `osquery::Status parseAliasData(const std::string& data) {`

if the path exists you can do `return Status(0, possible_file)` and if it doesn't you can return `return Status(1, "No file")` or something